On Wednesday, NASA’s Cassini mission will make the first of three close encounters with Enceladus, the sixth-largest of the moons of Saturn. The three close passes, which will be concluded by the end of the year, are set to provide the first opportunity for a close-up look at the north polar region of Enceladus when imagery is beamed back to Earth.
Enceladus is one of only three outer solar system bodies (along with Jupiter’s moon Io and Neptune’s moon Triton) where active eruptions have been observed.
It has been reported that analysis of the outgassing suggests that it originates from a body of sub-surface liquid water, which along with the unique chemistry found in the plume, has fueled speculations that Enceladus may be the most habitable spot beyond Earth in the Solar System for life.
Most of the data and photography from visiting spacecraft has been acquired by the Voyager 2 and Cassini spacecrafts.
Now that the summer sun is shining on the high northern latitudes, scientists will be looking for signs of ancient geological activity similar to the geyser-spouting, tiger-stripe fractures in the moon’s south polar region.
Features observed during the flyby could help them understand whether the north also was geologically active at some time in the past.
“We’ve been following a trail of clues on Enceladus for 10 years now,” noted Bonnie Buratti, a Cassini science team member and icy moons expert at NASA JPL. “The amount of activity on and beneath this moon’s surface has been a huge surprise to us. We’re still trying to figure out what its history has been, and how it came to be this way.”
Mission scientists announced evidence in March that hydrothermal activity may be occurring on the seafloor of the moon’s underground ocean. In September, they broke the news that its ocean – previously thought to be only a regional sea – was, in fact, global.
Wednesday’s flyby is considered a moderately close approach for Cassini, which will pass at an altitude of 1,142 miles (1,839 kilometers) above the moon’s surface. Closest approach to Enceladus will occur at 6:41 a.m. EDT (3:41 a.m. PDT). The spacecraft’s final two approaches will take place in late October and mid-December.
Images are expected to begin arriving one to two days after each of the flybys.
The Oct. 14 encounter will serve as a prelude to the main event, a flyby of Enceladus on Wednesday, Oct. 28, during which Cassini will come dizzyingly close to the icy moon, passing a mere 30 miles (49 kilometers) above the moon’s south polar region.
During this encounter, Cassini will make its deepest-ever dive through the moon’s plume of icy spray, collecting images and valuable data about what’s going on beneath the frozen surface.
Cassini scientists are hopeful data from that flyby will provide evidence of how much hydrothermal activity is occurring in the moon’s ocean, and how the amount of activity impacts the habitability of Enceladus’ ocean.
“The global nature of Enceladus’ ocean and the inference that hydrothermal systems might exist at the ocean’s base strengthen the case that this small moon of Saturn may have environments similar to those at the bottom of our own ocean,” added Jonathan Lunine, an interdisciplinary scientist on the Cassini mission at Cornell University in Ithaca, New York.
“It is therefore very tempting to imagine that life could exist in such a habitable realm, a billion miles from our home.”
Major interest throughout the Agency was evident when the moon even gained a mention in Space Launch System (SLS) documentation.
The overview claimed the monster rocket could provide an opportunity to utilize its superior performance to race a large spacecraft to Enceladus on an ambitious sample capture mission.
SLS managers have continued working with JPL on potentially providing the ride for a proposed Europa mission, but a mission to Enceladus – along with a Mars Sample Return mission – have also gained documented references.
“The SLS could potentially enable sample return from Jupiter’s moon Europa because it would have the payload capacity to provide shielding for a lander on the surface, and sufficient fuel for propulsive maneuvers out of the gravitational well of Jupiter,” noted the Con Ops (Concept of Operations) presentation.
“At Enceladus, a small active moon of Saturn, the SLS could carry the fuel needed to slow down for sample capture from the plumes on Enceladus, or create an artificial plume on either Europa or Enceladus by firing a copper projectile at the surface.”
Such a mission was only provided an example, with the SLS team attempting to promote SLS capability, as opposed to announcing a mission planning phase.
For the meantime, NASA is already in touching distance of the moon, as Cassini presses on with its own observations.
Cassini’s final close flyby on Dec. 19 will examine how much heat is coming from the moon’s interior from an altitude of 3,106 miles (4,999 kilometers).
“We’ll continue observing Enceladus and its remarkable activity for the remainder of our precious time at Saturn,” added Linda Spilker, Cassini project scientist at JPL.
“But these three encounters will be our last chance to see this fascinating world up close for many years to come.”
(Images via NASA and L2 artist Nathan Koga – The full hi-res gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)
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